1. INTRODUCTION
As energy demands increase and the associated costs increasing with demand, newer energy alternatives are becoming more important to society and also consumers want an uninterrupted and economical electric power. Recently, distributed generation (DG) has become an attractive method of providing electricity to consumers and retailers. In addition, from the viewpoint of economic feasibility, the costs of installing generators and producing the electricity can be comparatively inexpensive using the DG method.
One of DG sources is Microturbine Generation systems. Microturbine generator systems are those generator systems equipped with small combustion turbines approximately the size of a refrigerator with outputs of 25kW to 500kW.They operate at a high speed generally in the range of 50,000 to 120,000rpm.Electric power is produced in the range of 1400-4000Hz.They are most suitable for small to medium-sized commercial and industrial loads. The microturbine provides input mechanical energy for the generator system which is converted by the generator to electrical energy. The electrical energy is later converted to normal supply frequency and passed through the transformer, is delivered to the distribution system and the local load.
The microturbine generators come under the Distributed Energy Resources. Device category. Those devices enable renewable energies utilization and more efficient utilization of waste heat in combined heat and power (CHP) applications and lowering emissions. Unlike traditional backup generators, microturbine generators are designed to operate for extended periods of time and require little maintenance. They can supply customer’s base-load requirements or can be used for standby, peak shaving and cogeneration applications.
As microturbine generators don’t have reciprocating parts, there is no need of lubricating and all. Some microturbines even utilize air bearings and air cooling, thereby completely eliminating the need to change and dispose of hazardous liquid lubricants and coolants. In any case, microturbines are similar to major power plants, able to run for extended periods at full power output, and require little scheduled maintenance compared with traditional reciprocating engine generators of similar size. This makes them ideal for stationary prime power applications. The combustion process in a microturbine is continuous and clean burning, similar to modern gas turbine power plants. Microturbine manufacturers have deployed state of the art lean-burn combustion technology to control emissions without the need for expensive catalytic exhaust reatment equipment or chemicals.2. MICROTURBINE GENERATOR
Microturbine generators(MTG) are small, high speed power plants that are usually include the turbine, compressor and power electronics to deliver the power to the grid. These small power plants typically operate on natural gas. Future units may have the potential to use lower energy fuels such as gas produced from landfill or digester gas. Microturbine generators are classified into two types:
 Unrecuperated (simple cycle) microturbine generators.
 Recuperated microturbine generators.2.1 UNRECUPERATED MTG
In a simple cycle or unrecuperated systems the compressed air is mixed with fuel and burned under constant pressure conditions. The resulting hot gas is allowed to expand through a turbine to perform work. Simple cycle MTGs have lower efficiency at around 15%, but also lower capital costs, higher reliability and more heat available for co-generation applications than recuperated units.2.2 RECUPERATED MTG
Recuperated units use a thin sheet-metal heat exchanger that recovers some of the heat from an exhaust stream (1,200ºF) and transfers it to the incoming air stream, boosting the temperature of the air stream (around 300ºF) supplied to the combustor. Further exhaust heat recovery can be used in a co-generation configuration. The fuel-energy to electrical conversion efficiencies are in the range of 20 to 30%. In addition, recuperated units can produce 30 to 40% fuel savings from preheating. Depending on the microturbine operating parameters, recuperators can more than double machine efficiency. 3. TECHNICAL BACKGROUND
The entire microturbine generator system can be divided into three primary sub-systems:3.1 Mechanical
The mechanical system comprises the turbine, generator, compressor and recuperator. The compressor-turbine package is the heart of the microturbine generator system. They are commonly mounted on a single shaft along with the electric generator. Two bearings support the single shaft. The microturbine generator system produces electrical power via a high speed generator turning on the single turbo-compressor shaft. The high-speed generator of the single-shaft design employs a permanent magnet (typically Samarium Cobalt) alternator, and requires that the high frequency AC output (about 1400Hz-4000Hz) be converted to 50Hz for the general use. They operate at cool, clean, low-vibration, environment and offers 160,000 hours of normal service.